Method of tanning hectograph copying pads



Patented Dec. 17, 1935 UNITED. STATES,

METHOD or TANNING nno'rodaarn corrmc. raps William B. Whitmore, Chicago, 111., assignor to Ditto, Incorporated, Chicago, 111., a corporation of West Virginia No Drawing. Application August 11, 1933, Serial No. 684,765

This invention relates to an improved method of tanning or hardening hectograph copying pads, or like gelatinous masses.

Copying surfaces have long been treated with 5 various tanning agents for the purpose of rendering the product tougher, more resistant to heat, more lasting in operation-and less tacky. Some agents such as formaldehyde are recognized to be rapid in their action, but their use 7 10 is attended with difficulty in that control is vuncertain, the mass is likely to become too viscous,

or have its melting point raised too far before application to a backing material can be completed, and-thus become unfit for use, and the 5 final product is then under the best conditions -not thoroughly suitable.

The slowly acting agents such as chrome alum and dichromates are easier.to control, but take a very considerable length of time to complete 20 the reaction. The tanning operation may require several months to be fully completed. The manufacturer is therefore forced to choose between having his product under-tanned at the outset, over-tanned before it is worn out, or else' 25:1 waiting several months before selling his product. Generally a compromise is reached under which the mass is somewhat.under-tanned in the beginning. and 'becomes over-tanned before otherwise wearing out. An over-tanned hectograph pad is unfit for use, however.

, It has now been discovered that a light-sensi- =1; tive slow-acting tanning agent may be applied to the gelatin mass and the tanning action accelerated by the use of strong li ht, particularly 4Q fold. It is possible under this process to prepare special orders for special localities, which was impracticable where the material had to be stored several months before use. Even more important, however, is the basic improvement in 50 the of the gelatin, which is considerably more flexible in operation and absorbs water with greater facility.

The reason. for this improved characteristic .of i

the product is -not fully understood, but is be- 55 lieved toj be (111g [50 the fact that under the 11 Claims. (01, 41-315 former processes the water present in the mass dried out to a very considerable extent before the tanning operation became complete. During the drying-out process the size of the gelatin cells likewise decreased so that when the tan- 5 ning'or hardening operation was finished, the size of the cells was permanently fixed ,at this decreased level. On the other hand, when the tanning operation is carried out rapidly the size of the cells is unchanged. The evaporation of water subsequently, therefore, simply results in the collapse of the large cell walls, and upon subsequerit moistening water is readily absorbed and the cells go back to their original size. The thickness of the large cell walls will of course in? be'less than that of the small ones, which wil.f likewise increase the ability of the mass to take up water rapidly.

As an example of the invention, a hectograph copying mass is prepared, for example, from one part of gelatin, four parts of water, 10 parts of glycerine, and 0. 005 part of ammonium dichromate. After the mass has been applied to the backing material it is submitted to strong light, preferably regulated artificial light such as is produced by a carbon are. A mercury quartz lamp used at a distance of 1% to 2 feet over a period of 5 to 15 minutes, depending on the thicknessof the band, will substantially complete the tanning operation. The exact time may readily be controlled by those skilled in the art both from the feel of the material andby the disappearance of the green color which is formed at the beginning of the tanning operation.

In place of the ammonium dichromate other alkali dichromates such as potassium and sodium may beemployed.

The invention is. likewise usable with other copying masseaandzalso for gelatin used for sizing paper. A typical example of a mixture' suitable for the latter purpose is 1 part glue, 4 parts water, 'l.parts glycerine and 0.008 parts ammonium dichromate. This mixture is ,applied to the paper and then with 5 strong light as previously described.

" By-copyingmad as used herein-is meant not only a short pad, but other copying surfaces re, gardless of proportion or form.

The foregoing detailed description has been .given for clearness of understanding only, and

no; unnecessary limitations should be understood therefrom, but the appended claims should be construed as broadly as permissible, in view of the prior art.

2. The method or forming stabilized hectograph cop surfaces which comprises forming a gelatinous mass containing a gelatin substance, water and glycerine wherein the proportion of glycerine exceeds the proportions of gelatin substance and of water, adding a minute proportion oi. a light-sensitive tanning agent to said gelatin mass and substantially completing the tanning reaction with the aid of light in a period less than one week.

3. The method of forming stabilized hectograph com ng surfaces which comprises forming a gelatinous mass containing a gelatin substance, water and glycerine wherein the proportion oi glycerine exceeds the proportions of gelatin substance andoi water, adding a light-sensitive tanning agent to said gelatin mass in amount not greater than about basedonthegelatinandcarryingoutthetanning reaction substantially solely under the.influence or light.

4. The method as set forth in claim a in which the light is strong in the ultra violet component.

5. The method of forming stabilized hectograph copying surfaces which comprises forming a gelatinous mass containing a gelatin substance, water and glycerine whereinthe proportion of glycerine exceeds the proportions of gelatin substance and oi! water, incorporating a minute proportion of a dichromate taming agent in said gelatin mass and subjecting the mixture to the action of concentrated light for a period suillcient to substantially complete said tanning 6. The method as set forth in claim 5, in which saidtanningreactioniscarried outsubstantially solely under the influence of light.,

reaction by the application or strong light for a period sumcient to substantially complete said reaction.

9. The method of preparing stabilized hectograph copying surfaces which comprises preparing an aqueous gelatin base mass containing a major proportion of glycerine, app y said mass to a sheet oi! backing material and tanning said gelatin base mass under the influence of a minute proportion of a tanning agent having a non-reversible tanning action upon said gela e tin, said tanning reactionbeing carried to stantial completion without the evaporation of a substantial quantity of moisture from said gelatin mass.

'l0. A hectograph copying pad comprising a backing material impregnated with hardened gelatin base mass comprising gelatin, a softening agent and a minute proportion of a light-active so hardening agent,- said, mass being stable to the action of moderate heat and under absorption and evaporation of water, and the cells of said gelatin mass being of substantially the same and wall thickness as when originally applied thereto.

11. A hectograph copyi pad co risin a backing material impregnated with a gelatin base mass including a minute proportion of a-. dichromate tanning agent not greater about 9% basedonthegelatincontainedinsaid mass, said gelatin having the characteristics resulting from promptly subjecting said mass to the action 01' strong ultra violet light until the tanning reaction is substantially complete andbeing substantially stabilized with respect to further hardening oversubstantial periodsottimeunder' conditions of use;

wiiuauawm'monn. 

